a) Field of the Invention
This invention relates to a method and apparatus for removing an indoor volatile organic substance, and more specifically to a method and apparatus for removing an indoor volatile organic substance, especially methanal (formaldehyde) or the like given off by bakeout (which will be described subsequently herein) or the like, which features treatment of the volatile organic substance in a closed system without ventilation by using a catalyst capable of oxidizing the volatile organic substance into carbon dioxide and water.
b) Description of the Related Art
From the viewpoint of energy saving or the like, a measure has been taken in recent years to make improvements in the air tightness of houses, offices and the like. As a result, this has, however, led to deterioration in the quality of indoor air due to less frequent air changes. This deterioration has now come to be known as so-called sick building syndrome, chemical substance anaphylaxis and the like, and is increasingly becoming an issue.
In particular, volatile organic substances (methanal, namely, formaldehyde and the like) contained in finishing materials, primers and structural materials for floors, walls and the like gradually evaporate into rooms after execution of works, and become a primary cause for deterioration in the quality of the indoor air of houses and the like having high air tightness.
As a measure for thoroughly overcoming such a problem, the use of construction materials which are free of volatile organic substances such as methanal (or which contain them at substantially reduced levels) may be contemplated. These construction materials are however costly and, under the current circumstances, a substantial amount of time will be needed until they are used widely.
Concerning houses already built with construction materials containing methanal or the like, there is a need to entirely replace such construction materials with non-methanal (or low-methanal) construction materials. Due to cost problems or the like, this is however practically almost unfeasible in many instances.
As a next best measure, it has hence been proposed to drive out and eliminate volatile organic substances by bakeout. The term "bakeout" means a method which comprises heating the interior of a room to 40.degree. C. or so under mechanical ventilation to forcibly release volatile organic substances, which still remain in finishing materials and the like, into the atmosphere. According to this method, conventional construction materials containing methanal or the like can be used as they are and, further, this method is also applicable to already built houses and the like.
The present applicant has already attempted to remove a volatile organic substance (specifically, methanal) by this method [see, for example, the Preprints of the 14th Air Cleaning and Contamination Control Research Conference, page 173 (1996); and the 15th Air Cleaning and Contamination Control Research Conference, page 187 (1997)]. Through these attempts, it has been ascertained that there is a correlation among the indoor temperature during bakeout, the surface temperature of a given construction material and the amount of a volatile organic substance given off from the construction material and that the amount of the volatile organic substance given off from the construction material abruptly increases with the surface temperature. Described specifically, a rise in the surface temperature as small as 3 to 5.degree. C. is sufficient to result in the release of a volatile organic substance at a rate about twice as would otherwise occur.
As is indicated in the above publications, an application of bakeout makes it possible to lower the concentration of methanal to significant extent in indoor air. For this method, however, mechanical ventilation is indispensable for the removal of evaporated methanal or the like. As a result, outdoor air flows in so that the indoor temperature drops. This temperature drop is unnegligibly substantial especially when the above method is conducted in winter or in a cold area.
Since the amount of methanal to be given off decreases abruptly with a drop in temperature as described above, sufficient removal effects may not be available where the temperature drops as a result of mechanical ventilation.
It is however actually difficult to set a higher temperature in expectation of such a temperature drop, because with construction materials forming a building or house, such as timber, there is a potential problem of strain and deformation developing due to uneven drying or the like.